How to make torque at higher RPM...
05-25-2006, 08:09 PM
#101
It seems that every said of constraints creates its own limits. Engine size, engine speed, forces on the reciprocating assembly, stabilty of the valvetrain, engine breathing, etc. Something is the limiting factor.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
05-25-2006, 08:42 PM
#103
TECH Fanatic
Originally Posted by DavidNJ
It seems that every said of constraints creates its own limits. Engine size, engine speed, forces on the reciprocating assembly, stabilty of the valvetrain, engine breathing, etc. Something is the limiting factor.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
There's no free lunch, and the combatants are smarter than the rules makers. Mother Nature is the real challenge. She has unbreakable, self-enforcing rules. NASCAR, NHRA and FIA are very jealous of her.
05-25-2006, 08:48 PM
#104
TECH Fanatic
Originally Posted by P Mack
That would be cool to see what engine combinations the teams came up with if engine speed or piston speed was limited instead of displacement.
If mean piston speed were limited to 5200 ft/min., about where it is now for Cup gear rule tracks, I'd wager a significant amount that bore/stroke sizes wouldn't change, unless the bore could be enlarged.
05-25-2006, 09:59 PM
#105
Originally Posted by Old SStroker
...limits inovation and technological development, limits competition, doesn't limit money spent however.
There's no free lunch, and the combatants are smarter than the rules makers. Mother Nature is the real challenge. She has unbreakable, self-enforcing rules. NASCAR, NHRA and FIA are very jealous of her.
There's no free lunch, and the combatants are smarter than the rules makers. Mother Nature is the real challenge. She has unbreakable, self-enforcing rules. NASCAR, NHRA and FIA are very jealous of her.
How are Hooter's Cup engines for cost of operation? I understand they have a size, bore, speed, and valve lift limit. Or ASA, which I believe requires crate motors? Or SCCA Spec Racer, which requires a crate motor purchased from and sealed by SCCA Enterprises?
05-26-2006, 12:17 AM
#106
FormerVendor
Originally Posted by DavidNJ
It seems that every said of constraints creates its own limits. Engine size, engine speed, forces on the reciprocating assembly, stabilty of the valvetrain, engine breathing, etc. Something is the limiting factor.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
Given that engine size is limited by rules, one of the others comes into play.
It seems like engine speed is a good one. Easy to maintain (similar to a transponder it seems), limits durability issues, limits power. Maybe we will see more of that.
Destroking makes no power at all but rather loses power.
Big bores can make more power than smaller bores since you can have bigger ports.
Destroking is only done since the displacement must remain constant otherwise you could make even MORE POWER if you could keep the stroke the same or increase stroke even further.
I only say this because some people in these threads are under the illusion that destroking does something positive to the engine.
Some people are also confused by the prevalence of certain strokes in the catalogues.
I was asked three times on this board and in PMs why no one makes destroker cranks for the LS1. I can only shake my head.
05-26-2006, 12:30 AM
#107
FormerVendor
Originally Posted by Old SStroker
Thanks for the reminder. Erik, meet joecar.
Yep, larger displacement engines can make more power if you do it right. No argument there.
I look at high piston speed as an enemy, not as a friend. Perhaps we differ there, EK.
With half the rpm wouldn't you need to make twice the torque to get the same power?
Are not mandated bore limits for a given displacement put there because with larger bores for a given displacement, the racers shorten the stroke so they can twist it higher and keep the inertia loads in check and not lose so much hp to ring friction? So why not just limit displacement and max stroke if stroke is where more power comes from?
Bore (or stroke) limits are often instituted when one group of guys make more power and/or rpm because their engine allows a larger dimension. eg. Chrysler's Cup block allowed 4.200 or so bores and made more power, but the other guy's blocks wouldn't allow that much bore, so 4.185 was the new max. allowed. You could run a 3.77 bore in a Cup engine with a 4.00 stroke and it would fit in all the blocks and NASCAR wouldn't say anything against it. You might have to notch the bores for the valves, of course. My guess is that it wouldn't be much of a threat for the pole, either.
With a displacement limit and a bore limit, you don't have to limit stroke; it's self limiting.
Wild guess here: 500 cubic inch NHRA maximum would be exceeded as stroke got much over 3.60 with the 4.700 bore.
791-815 cubes vs. 500 can make lots of torque if you do it right. You should be able to make lots more power with the larger engine, but not run into the huge inertia loads which are proportional to the square of the rpm but proportional only to the first power of the stroke. NHRA PS engines are horribly expensive, partly because the do run such high rpm for the size of the engine.
Let's see, maybe they want all the cubes the rules allow using the biggest bores they can.
Some of the F1 engine guys weren't real happy with the 98 mm max bore limit on the V8s. They had room for more bore spacing than the V10s had and still have a shorter engine. (Perhaps) they were looking at larger bores, shorter strokes, more rpm and more specific output, and Max Mosley got wind of that testing.
It's the "monkey see, monkey do" mentality in F1 and Cup. How boring (pun intended). The all run very similar bores and strokes. No inovation anymore.
Don't ask if you don't want my opinion.
Yep, larger displacement engines can make more power if you do it right. No argument there.
I look at high piston speed as an enemy, not as a friend. Perhaps we differ there, EK.
With half the rpm wouldn't you need to make twice the torque to get the same power?
Are not mandated bore limits for a given displacement put there because with larger bores for a given displacement, the racers shorten the stroke so they can twist it higher and keep the inertia loads in check and not lose so much hp to ring friction? So why not just limit displacement and max stroke if stroke is where more power comes from?
Bore (or stroke) limits are often instituted when one group of guys make more power and/or rpm because their engine allows a larger dimension. eg. Chrysler's Cup block allowed 4.200 or so bores and made more power, but the other guy's blocks wouldn't allow that much bore, so 4.185 was the new max. allowed. You could run a 3.77 bore in a Cup engine with a 4.00 stroke and it would fit in all the blocks and NASCAR wouldn't say anything against it. You might have to notch the bores for the valves, of course. My guess is that it wouldn't be much of a threat for the pole, either.
With a displacement limit and a bore limit, you don't have to limit stroke; it's self limiting.
Wild guess here: 500 cubic inch NHRA maximum would be exceeded as stroke got much over 3.60 with the 4.700 bore.
791-815 cubes vs. 500 can make lots of torque if you do it right. You should be able to make lots more power with the larger engine, but not run into the huge inertia loads which are proportional to the square of the rpm but proportional only to the first power of the stroke. NHRA PS engines are horribly expensive, partly because the do run such high rpm for the size of the engine.
Let's see, maybe they want all the cubes the rules allow using the biggest bores they can.
Some of the F1 engine guys weren't real happy with the 98 mm max bore limit on the V8s. They had room for more bore spacing than the V10s had and still have a shorter engine. (Perhaps) they were looking at larger bores, shorter strokes, more rpm and more specific output, and Max Mosley got wind of that testing.
It's the "monkey see, monkey do" mentality in F1 and Cup. How boring (pun intended). The all run very similar bores and strokes. No inovation anymore.
Don't ask if you don't want my opinion.
What you aren't seeing is that in your posts you are implying that there is something positive about destroking an engine when in reality the only positive thing is the bigger bore.
The bigger stroke engines turn LOWER rpm than the short stroke engines so they do not have the reliability problems in general that their short stroke higher rpm cousins do. You are often implying in your logic that both engines would be run at the same rpms and they would not.
If stroke wasn't actually helping engines but rather hurting them than they wouldn't limit the displacement either as any displacement gained by stroke alone must be hurting the engine according to most of your logic?
OR.... admit that the bigger bores make power because of the breathing they allow and destroking only hurts the engine but less than the bigger bore is helping it.
At a certain point the bore becomes too big again and teh stroke too short with a fixed displacement anyway and starts killing power because of the weight of the piston and bad cylinder seal and totally ridiculous bottom end loads brought on by low piston speed and super high rpm. Imagine a 5 inch bore and a .5 inch stroke if that's what it takes.
Big bore and short stroke is NOT an endless treasure trove of even hp/inch. At some point it starts even hurting rpm potential and power itself.
05-26-2006, 07:33 AM
#108
TECH Fanatic
Originally Posted by racer7088
Yeah I didn't see his post as I was still further up.
What you aren't seeing is that in your posts you are implying that there is something positive about destroking an engine when in reality the only positive thing is the bigger bore.
The bigger stroke engines turn LOWER rpm than the short stroke engines so they do not have the reliability problems in general that their short stroke higher rpm cousins do. You are often implying in your logic that both engines would be run at the same rpms and they would not.
If stroke wasn't actually helping engines but rather hurting them than they wouldn't limit the displacement either as any displacement gained by stroke alone must be hurting the engine according to most of your logic?
OR.... admit that the bigger bores make power because of the breathing they allow and destroking only hurts the engine but less than the bigger bore is helping it.
At a certain point the bore becomes too big again and teh stroke too short with a fixed displacement anyway and starts killing power because of the weight of the piston and bad cylinder seal and totally ridiculous bottom end loads brought on by low piston speed and super high rpm. Imagine a 5 inch bore and a .5 inch stroke if that's what it takes.
Big bore and short stroke is NOT an endless treasure trove of even hp/inch. At some point it starts even hurting rpm potential and power itself.
What you aren't seeing is that in your posts you are implying that there is something positive about destroking an engine when in reality the only positive thing is the bigger bore.
The bigger stroke engines turn LOWER rpm than the short stroke engines so they do not have the reliability problems in general that their short stroke higher rpm cousins do. You are often implying in your logic that both engines would be run at the same rpms and they would not.
If stroke wasn't actually helping engines but rather hurting them than they wouldn't limit the displacement either as any displacement gained by stroke alone must be hurting the engine according to most of your logic?
OR.... admit that the bigger bores make power because of the breathing they allow and destroking only hurts the engine but less than the bigger bore is helping it.
At a certain point the bore becomes too big again and teh stroke too short with a fixed displacement anyway and starts killing power because of the weight of the piston and bad cylinder seal and totally ridiculous bottom end loads brought on by low piston speed and super high rpm. Imagine a 5 inch bore and a .5 inch stroke if that's what it takes.
Big bore and short stroke is NOT an endless treasure trove of even hp/inch. At some point it starts even hurting rpm potential and power itself.
05-26-2006, 07:43 AM
#109
As long as you can provide air for it, the increase in displacement should help as long as it is within the current range of engines: bore from 2.5 to 4.5-5.0. stroke from 2 to 5, bore/stroke ratios of .75 to 2, rod/stroke ratios of 1.2 or so to 2.5 or so.
Beyond that you may run into problems with the combustion efficency dropping off, excessive side loads on the pistons, etc.
Finally, few engines don't have some packaging issue. The size and weight constraint then takes hold. We don't see that much in racing since most (all?) classes now have significnat engine rules. The last time I remember it was in the 1960's CanAm series. However, at that time fabrication costs were higher and some combustion design and control technology didn't exist.
Beyond that you may run into problems with the combustion efficency dropping off, excessive side loads on the pistons, etc.
Finally, few engines don't have some packaging issue. The size and weight constraint then takes hold. We don't see that much in racing since most (all?) classes now have significnat engine rules. The last time I remember it was in the 1960's CanAm series. However, at that time fabrication costs were higher and some combustion design and control technology didn't exist.
05-26-2006, 10:03 AM
#110
FormerVendor
Originally Posted by Old SStroker
I'm imagining a .5 inch bore with a 5 inch stroke....but the mind wanders.
05-26-2006, 10:24 AM
#111
TECH Fanatic
Originally Posted by Old SStroker
I'm imagining a .5 inch bore with a 5 inch stroke....but the mind wanders.
Originally Posted by racer7088
You're right Old SStroker that if you go too far either way you end up in lala land. It's a curve though with the bore stroke thing not just one way or the other and the curve changes depending on what you are after out of the engine.
I'm old, but not THAT old!
After all our discussions I considered changing my screen name to Old Bore, but that hits too close to home according to some folks. FWIW, my screen name comes from Stroker McGurk, a favorite character of my youth, and my offspring, 'Ace.
05-26-2006, 11:21 AM
#112
Now, would a 5L that turned 8500rpm be able to match a 6.3L that ran to 6500, yet be more efficient at part throttle, lower speed (say 2500rpm) operation? Admittedly, it wouldn't be any lighter unless it was designed that way from scratch, which none of our domestic OHV V8s are.
05-26-2006, 12:05 PM
#113
TECH Fanatic
Originally Posted by DavidNJ
Now, would a 5L that turned 8500rpm be able to match a 6.3L that ran to 6500, yet be more efficient at part throttle, lower speed (say 2500rpm) operation? Admittedly, it wouldn't be any lighter unless it was designed that way from scratch, which none of our domestic OHV V8s are.
If you want to do the calculations, let's assume a BMEP @ power peak of 170 psi for the 8500/5L and 180 psi for the 6500/6.3L because it's easier to make higher BMEP at lower rpm.
Given:
BMEP/150.8 = torque per cubic inch.
HP = torque x rpm/5252
torque = hp x 5252/rpm
1 L = 61 cubic inches (close enough)
Which engine makes more hp? How much?
Which would cost more to build? Why?
You do the math. I'm lazy.
(Show your work)
05-26-2006, 04:37 PM
#115
FormerVendor
Originally Posted by Old SStroker
I wasn't thinking about an engine. The mind was wandering to things anatomical that stroke, albeit fairly slowly.
I'm old, but not THAT old!
After all our discussions I considered changing my screen name to Old Bore, but that hits too close to home according to some folks. FWIW, my screen name comes from Stroker McGurk, a favorite character of my youth, and my offspring, 'Ace.
I'm old, but not THAT old!
After all our discussions I considered changing my screen name to Old Bore, but that hits too close to home according to some folks. FWIW, my screen name comes from Stroker McGurk, a favorite character of my youth, and my offspring, 'Ace.
Old Bore or Old SStroker we will still all love you anyway no matter what your name!
05-26-2006, 05:57 PM
#117
TECH Fanatic
Originally Posted by DavidNJ
Reminds me of some kittens I saw the other day.
So how's the "homework" coming?
05-27-2006, 06:54 PM
#118
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Old SStroker:
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.
And as far as stroke and bore - Let's take a 5L engine. It is better to make a 5L engine with a larger bore and a smaller stroke. The displacement is basically what determines the TQ and a shorter stroke allows for more rotations per minute. If a 5L engine had a smaller bore and a larger stroke, then it would have the same TQ but less RPM because the pistons would have to travel a further distance. Correct?
I'm not saying that stroking an engine is bad though. Stroking an engine increases your TQ by increasing displacement, you would probably lose RPMs a little but it is apparently by not as great amount as you increase your TQ. Otherwise, stroked engines would make less HP, which we all know they make more HP. These are the basics of what I think I undertstand, just checking to see if I am off-base or not. Thanks.
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.
And as far as stroke and bore - Let's take a 5L engine. It is better to make a 5L engine with a larger bore and a smaller stroke. The displacement is basically what determines the TQ and a shorter stroke allows for more rotations per minute. If a 5L engine had a smaller bore and a larger stroke, then it would have the same TQ but less RPM because the pistons would have to travel a further distance. Correct?
I'm not saying that stroking an engine is bad though. Stroking an engine increases your TQ by increasing displacement, you would probably lose RPMs a little but it is apparently by not as great amount as you increase your TQ. Otherwise, stroked engines would make less HP, which we all know they make more HP. These are the basics of what I think I undertstand, just checking to see if I am off-base or not. Thanks.
05-28-2006, 02:43 AM
#119
FormerVendor
Originally Posted by Louie83
Old SStroker:
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.
And as far as stroke and bore - Let's take a 5L engine. It is better to make a 5L engine with a larger bore and a smaller stroke. The displacement is basically what determines the TQ and a shorter stroke allows for more rotations per minute. If a 5L engine had a smaller bore and a larger stroke, then it would have the same TQ but less RPM because the pistons would have to travel a further distance. Correct?
I'm not saying that stroking an engine is bad though. Stroking an engine increases your TQ by increasing displacement, you would probably lose RPMs a little but it is apparently by not as great amount as you increase your TQ. Otherwise, stroked engines would make less HP, which we all know they make more HP. These are the basics of what I think I undertstand, just checking to see if I am off-base or not. Thanks.
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.
And as far as stroke and bore - Let's take a 5L engine. It is better to make a 5L engine with a larger bore and a smaller stroke. The displacement is basically what determines the TQ and a shorter stroke allows for more rotations per minute. If a 5L engine had a smaller bore and a larger stroke, then it would have the same TQ but less RPM because the pistons would have to travel a further distance. Correct?
I'm not saying that stroking an engine is bad though. Stroking an engine increases your TQ by increasing displacement, you would probably lose RPMs a little but it is apparently by not as great amount as you increase your TQ. Otherwise, stroked engines would make less HP, which we all know they make more HP. These are the basics of what I think I undertstand, just checking to see if I am off-base or not. Thanks.
This in turn allows you to lower you gear ratio in the axle since the engine can now spin higher in rpm up there which also mutlplies your RWTQ even higher which is what accelerates your car faster. Either way F=MA so you need more RWTQ or less mass in the car to go faster.
If I can double the rpm I am making that same TQ at then I can use a gear twice as low so I will now have twice the TQ at the wheels even though my engine tq is the same. Same thing if you have too much RWTQ you can run a taller gear and knock that down.
05-28-2006, 08:49 AM
#120
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Originally Posted by Louie83
Old SStroker:
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.
I can see why you want to make more TQ at higher RPMs than lower; because HP = TQ x RPM / 5250 therefore, you will make more total HP making 300 lb/ft from 4000-7000 RPM than from making 300 lb/ft from 2000-5000 RPM. But how does it help you take advantage of gearing, like that Reher guy was saying? I'm confused on that part.